1. Field of the Invention
In the machine tool field it is common to secure movable elements of such tools with a clamping-type locking device. The jaws of such clamps are commonly expanded and contracted by the use of a threaded actuator in which the threads have a sufficiently large pitch that a few degrees of revolution of the actuator will clamp or unclamp the element to be held.
Exemplary of such machines is the Bridgeport-type milling machine wherein the quill housing encircles a spindle, which carries a cutting tool. The spindle is moved longitudinally in or out of the quill housing to control the position of the cutting tool and to advance the tool into, and away from, the work piece for operations such as boring, drilling, reaming, or tapping.
In order to fix the position of the spindle, a screw-type locking device, commonly referred in the industry as a quill lock, is used on such machines to clamp the spindle in place when linear movement is to be prevented.
In a typical case, the quill lock is actuated by a small handle that extends radially outwardly from the screw portion at right angles. Such devices pose a problem, however, to the operator, which was apparently never considered by the manufacturer to be a concern in use. Specifically, the quill lock does not always fully release when the locking lever is in the release position, or may move from the release position to a partially locked position, due to downward forces generated on the screw portion of the lock by the protruding lever which, for safety reasons, is normally in a raised portion.
This movement occurs due to gravitational pull, which tends to urge the lever downwardly toward the locked position. As a result of such movement, a drag is created on the spindle as the operator tries to advance or retract it during operation. This tendency to self tighten, not only interferes with the smooth operation of the spindle stroke, but becomes a distraction to the operator, who may try to fight the quill lock at the same time as he is operating the machine, and in so doing, lose concentration, to the detriment of the job and perhaps his personal safety.
2. Overview of the Prior Art
Several prior art patents have been unearthed which pertain to machine tools that employ quill and locking devices therefor. These prior art patents are, however, more illustrative of the problem than the solution, and none of them specifically address the environment of the present invention, or the relief that it offers for the problem addressed.
By way of example, Wood U.S. Pat. No. 4,175,898 depicts a machine tool of the general type for which the present invention has particular utility. However, the inventor was primarily concerned with locking and unlocking the tool holder, which he accomplishes by means of a powered drawbar.
Fox U.S. Pat. No. 4,349,945 relates to a horizontally disposed machine tool, having essentially the same mechanism, disposed in a different attitude, but the problem remains the same. Again, the Fox disclosure does not address the problem, but rather has as its focus a power head locking device.
The Kampmeier U.S. Pat. No. 2,957,393 relates to a hydraulic clamping device, which is an alternative to the more common mechanical devices. The Csencsics U.S. Pat. No. 3,586,455 employs pneumatics to move the quill, and, at least to that extent, alleviates the problem addressed herein. The patents to Vincent, U.S. Pat. No. 3,003,412; Sedgwick, U.S. Pat. No. 3,457,833, and Lehman U.S. Pat. No. 4,209,273 all reflect, in a general sense, the state of the art in machine tools, without addressing the problem referenced by the present invention.
Bridgeport-type machine tools have been in use for a number of years, and the problem of drag on the spindle due to the quill lock has existed for the same period, yet until now an adequate and safe solution has evaded the industry.
Indeed, until the advent of the present invention, machinists have attempted to address the problem of quill drag by manually holding the lock lever up with one hand while operating the quill feed handle with the other. The biggest disadvantage to this method is that it requires the use of both hands and does not allow the operator to use a hand to hold onto the work piece, or fixture, when using the mill as a drill press for drilling and tapping.
More innovative operators have found that the lock lever can be held in the unlocked up position by wrapping a rubber band around the lever and attaching it to a nut, or other protuberance, on the mill head in order to retain the lever in the "up", or unlocked, position during operation. However, like most "make shift" cures, there are drawbacks, and in this case the rubber bands tend to fly off and/or wear out quickly in the oily environment. When the rubber band lets go, particularly during operation, a potentially dangerous situation is created.
The industry has seen other devices to cure this problem, although it does not appear that they are patented. For example, a device called the "Quill Free" is available, and operates similar to the rubber band method. It consists of mounting hardware to fasten a tension spring between the lever and a nut, or other mounting device, on the mill head. The tension of the spring keeps the lever in the unlocked position.